ITHACA, N.Y. — It’s probably not something you want to think about while digesting your Easter dinners, but you’ll want to keep the rock salt and shovels handy as a spring snowmaker traverses across the Southern Tier Monday night. However, don’t put the tee shirts and sun dresses away, because some milder conditions are in store for the second half of this week.

Your Weekly Weather

Last week’s slow-moving but powerful Canadian storm system has finally shuffled eastward over Atlantic Canada, and behind the low, substantial amounts of cold polar air are being advected southward in its counterclockwise circulation. A few instability showers persist in the broader circulation of the low, but most have withered away, leaving partly cloudy conditions and a rather brisk April day with northwest winds and highs in the mid 40s.

As the storm system continues to move away to the east, Canadian high pressure with build in from the northwest. This will result in a cold but quiet night, with mostly clear skies, calm winds and a low in the upper 20s.

High pressure shifts eastward for Monday, and clouds will rapidly build in during the morning ahead of the next storm system. It’s a fairly standard winter storm setup – a system dropping in over the Great Lakes interacts and later merges with a developing storm system moving up the East Coast. That injection of energy and a favorable upper-air setup will enhance the coastal system’s development as it moves onto land over Southern New England and continues northeastward.

This storm will be very topographically dependent as the key factor is how much cold air and how long it’s in place. In Ithaca, it’ll be overcast and around 50°F by mid-afternoon with rain likely to start in the 2-5 PM range; this won’t change over to snow until temperatures later Monday night, with the loss of daytime heating and as the coastal low strengthens and draws in more cold air. However, up on the hills temperatures won’t get as warm during the day Monday. The change over to snow will be sooner, when more of the precipitation shield has yet to pass, and some embedded more intense snow bands are likely east of Ithaca overnight. It is quite likely that valley and lakeshore locations like Ithaca get only a coating by the time the snow tapers off mid-morning Tuesday, while the hills, especially east of Ithaca in Dryden and Caroline, see 4-6″.

Tuesday will remain unsettled, with snow showers changing back over to rain with daytime heating late Tuesday morning. Expect intermittent rain to continue for the remainder of the day with gusty west winds and highs in the low 40s. Temperatures are unlikely to fall much Tuesday night as the storm rapidly moves away and high pressure builds in from the Ohio River Valley. Rain will taper off after sunset, maybe with a few token snow showers, with clearing skies after midnight and lows in the mid 30s.

Wednesday will be a much nice and more seasonable day, if still a tad cooler than normal, as the high pressure continues to work in from the southwest. There will be a few passing clouds with highs in the mid 50s. Wednesday night will see increasing clouds as the frontal boundary of a Canadian storm system begins to approach from the west, though it should stay dry overnight with lows in the upper 30s.

Thursday is by no means a washout. The storm will pass far to the north and there will be a lack of moisture; this will mostly be a cloud producer with a few scattered showers in the late morning and afternoon. The storm should generate enough southerly flow ahead of it to warm up temperatures even with the near-overcast skies, topping out in the mid 60s. Clouds will decrease overnight and the winds should shift to the northwest in the early hours of Friday morning. Overnight lows Thursday will be in the low 40s.

Friday sees another brief bubble of high pressure build in from the northwest. It will be partly cloudy with highs in the mid 60s. Friday night will see increasing clouds as a storm system develops well to the west of Tompkins County, with dry conditions overnights and lows in the upper 40s.

The weekend is looking warm and pleasant, as that storm system stays off to the west but conjures up ample southerly flow over the Eastern United States. Expect partly cloudy skies both Saturday and Sunday with highs around 70 Saturday and in the mid 70s Sunday. Lows will be in the low 50s.

Graphics courtesy of the NOAA Climate Prediction Center.

Extended Outlook

Looking into the last week of April, the large scale pattern favors a roughly zonal jet stream that tends to keep cold air bottled up in the northern latitudes and warmer air to the south, though with some weak ridging over the Southwest and troughiness over the Great Lakes. The pattern favors somewhat cooler than normal conditions for Tompkins County, with near-average precipitation.

Brian Crandall

Brian Crandall reports on housing and development for the Ithaca Voice. He can be reached at bcrandall@ithacavoice.com.